Protective helmet



FIG. 1 is a top, front and side perspective view of a protective helmet showing my new design;

FIG. 2 is a side elevational view thereof, the opposite side being a mirror image;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a front elevational view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a rear elevational view thereof. 

The ornamental design for a protective helmet, as shown and described. 